1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a storage medium.
2. Description of the Related Art
A moving-type image reading unit in an image reading apparatus typified by a conventional flatbed image reading apparatus moves while increasing the speed of a carriage up to an effective readable range. The image reading unit reads the density of a white reference plate while moving to generate shading data for correcting shading (refer to Japanese Patent Application Laid-Open No. 4-265070). A stationary-type image reading unit in an image reading apparatus typified by a sheet-through image reading apparatus reads the density of a white reference plate or a white roller arranged on a surface facing the stationary image reading unit to generate shading correction data for correcting shading.
In Japanese Patent Application Laid-Open No. 4-265070, since the image reading unit reads the white reference plate while moving in parallel with the white reference plate, no matter where the image reading unit is moved, reading of the white reference plate exhibits a constant value. However, if the image reading unit cannot move in parallel with the white reference plate, the reading value obtained from the white reference plate changes depending on a positional relationship between the image reading unit and the white reference plate. For example, the longer the distance between the image reading unit and the white reference plate, the smaller the luminance value obtained by reading the white reference plate.